题解：P12006 【MX-X10-T2】[LSOT-4] 网易云

#include<bits/stdc++.h>
#define int long long
#define inf 0x7f7f7f7f
using namespace std;
const int maxn = 100010;
inline int read() {
	int x=0,f=1;char ch=getchar();
	while (ch<'0'||ch>'9'){if (ch=='-') f=-1;ch=getchar();}
	while (ch>='0'&&ch<='9'){x=x*10+ch-48;ch=getchar();}
	return x*f;
}
int n , m , a[maxn] , tong[maxn];
signed main() {
	n = read();
	m = read();
	for(int i = 1; i < n; i++) a[i] = read();
	for(int i = 1; i <= m; i++) {
		int u = read() , v = read();
		tong[u] += v;
	}
	int ans = 0;
	for(int i = 1; i < n; i++) {
		ans += tong[i] * a[i];
		tong[i + 1] -= tong[i];
		tong[i] -= tong[i];
	}
	for(int i = 1; i <= n; i++) {
		if(tong[i]) {
			cout << "Impossible" << endl;
			return 0;
		}
	}
	cout << ans << endl;
	return 0;
}